Hydrostatic pumps are frequently constructed in such a way that they can be driven in two directions. If, however, the rotational direction of the drive is reversed, the delivery direction is also reversed. It is therefore frequently required to ensure rectification of the volumetric flow which is produced. This means that a suction-side connection and a delivery-side connection of the entire pump unit retain their function even in the case of a change in the rotational direction of the pump. For this purpose, it is known to arrange four valves in what is known as a Graetz circuit. Here, as is shown in DE 42 34 139 C2, a first suction valve is arranged between a first pump connection and the suction-side connection of the pump unit and a second suction valve is arranged between a second pump connection and the suction-side connection of the pump unit. Furthermore, a first pressure valve is arranged between the second pump connection and a delivery-side connection of the pump unit and a second pressure valve is arranged between the first pump connection and the delivery-side connection of the pump unit. Depending on the delivery direction, the pump then delivers toward the first pump connection or the second pump connection, whereas it sucks in pressure medium at the respectively other pump connection. For example, in the case of a first delivery direction, pressure medium is sucked in from the suction-side connection of the pump unit via the first suction valve and is sucked in by the pump at the first pump connection. The pump delivers toward the second pump connection, with the result that the pressure medium is fed via the first pressure valve to the delivery-side connection of the pump unit. On account of the pressure conditions which are produced, in contrast, the second suction valve and the second pressure valve are moved into their closed position and are held there by the delivery pressure.
It is problematical in the case of the proposed valve arrangement that in the case of jamming or sticking in the described case example of the first suction valve which is opened only by the vacuum, the pressure medium which is conveyed by the pump toward the delivery-side connection cannot be replenished. This can lead to damage of the pump. The valve arrangement which is described here is preferably arranged in a connection plate of a hydrostatic piston machine and forms a pump unit together with the latter. In order then to make the opening of the suction valve to be opened possible reliably, it is already known to connect the valve bodies of the two suction valves to one another. As a result, one of the two valves is always open. The force which is exerted in the closing direction by the delivery pressure on the suction valve which is connected to the delivery-side pump connection is therefore used to open the suction valve which is connected to the suction-side pump connection. However, this variant has the disadvantage that jamming of the connecting rod or the valve bodies which are connected thereto can occur.
It is therefore the object to provide a valve arrangement, a connection plate and a hydrostatic piston machine, in which reliable opening of the suction valve which is situated on the respective suction side is ensured.
The object is achieved by the valve arrangement according to the disclosure, the connection plate and the corresponding hydrostatic piston machine.